CN115020710A - Low-expansion silicon-based composite negative electrode material, preparation method thereof and lithium ion battery - Google Patents
Low-expansion silicon-based composite negative electrode material, preparation method thereof and lithium ion battery Download PDFInfo
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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Abstract
The invention relates to a low-expansion silicon-based composite negative electrode material, belonging to the technical field of lithium ion batteries. Low silicon-based composite negative electrode material of inflation, including the kernel and the shell of cladding on the kernel, the shell includes endocyst cladding, well cladding, the outer cladding that sets gradually from inside to outside, and the endocyst cladding is amorphous carbon layer A, and well cladding is solid electrolyte layer, and the outer cladding is amorphous carbon layer B, and the quality of shell accounts for the 5-15% of low silicon-based composite negative electrode material of inflation quality. The low-expansion silicon-based composite negative electrode material greatly reduces the expansion of the silicon-based composite material, and fundamentally improves the cyclicity of the silicon-based negative electrode material.
Description
Technical Field
The invention relates to a low-expansion silicon-based composite negative electrode material, belonging to the technical field of lithium ion batteries.
Background
In recent years, with the rapid expansion of the electric vehicle market, the demand of the market for the energy density of the lithium ion battery is higher, and the development is focused on the improvement of the energy density of the positive electrode material and the energy density of the negative electrode material.
The silicon-based material has a hot point for research and development due to the ultrahigh theoretical energy density (4200mAh/g), but the problems of volume expansion and poor electronic conductivity of the silicon-based material always restrict the scale application of the silicon-based negative electrode material. Poor electronic conductivity can result in a cell with low first efficiency, volume expansion can result in very poor cycling performance and poor rate performance, and capacity fade is too fast. In order to solve the above problems of the silicon-based materials, the methods adopted in the prior art are to nanocrystallize the silicon-based materials, and coat the surface of the materials to reduce the impedance of the materials and reduce the expansion thereof, such as coating the surface of the materials with amorphous carbon, solid electrolyte and the like to restrict the expansion in the charge-discharge process.
Chinese patent application publication No. CN112467115A discloses a silicon-carbon composite material, which includes an inner core and an outer shell covering the inner core; the inner core comprises nano silicon material; the material of the housing includes carbon and a lithium-containing solid electrolyte. Although the silicon-carbon composite material can reduce impedance, improve the first efficiency and reduce expansion, the full-electricity expansion of the material is large because the inner core and the outer shell are physically combined, and the cycle performance is still to be improved.
Disclosure of Invention
The invention provides a low-expansion silicon-based composite negative electrode material, a preparation method thereof and a lithium ion battery, which are used for improving the cycle performance of the silicon-based composite negative electrode material.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the utility model provides a low inflation silicon-based composite negative pole material, includes the kernel and the shell of cladding on the kernel, and the shell includes interior cladding, well cladding, the outer cladding that sets gradually from inside to outside, and the interior cladding is amorphous carbon layer A, and well cladding is the solid electrolyte layer, and the outer cladding is amorphous carbon layer B, and the quality of shell accounts for the quality of low inflation silicon-based composite negative pole material 5-15%.
A preparation method of a low-expansion silicon-based composite anode material comprises the following steps:
1) soaking the silicon powder in hydrofluoric acid for 2-5h, and carrying out solid-liquid separation to obtain porous silicon;
2) uniformly mixing the porous silicon obtained in the step 1), a silane coupling agent and a carbon nano tube in an organic solvent, and then carrying out carbonization treatment to obtain a composite material A; the carbonization treatment is carried out for 3-5h at the temperature of 750-800 ℃ in inert atmosphere;
3) uniformly dispersing the composite material A obtained in the step 2), a dispersing agent and a solid electrolyte in an organic solvent, and then carrying out spray drying to obtain a composite material B; the solid electrolyte is
4) Preserving the temperature of the composite material B obtained in the step 3) in a carbon source mixed gas at 700-; the carbon source mixed gas is formed by mixing at least one of methane, ethylene and acetylene with ammonia gas according to the volume ratio of 100: 1-10.
The particle size of the silicon powder in the step 1) is 100-500 nm.
The mass fraction of the hydrofluoric acid in the step 1) is 1-10%.
In the step 2), the mass ratio of the porous silicon to the silane coupling agent to the conductive agent is 100: 1-5: 0.5-2.
In the step 2), the porous silicon, the silane coupling agent and the carbon nano tube are uniformly mixed in the organic solvent, and the porous silicon and the carbon nano tube are added into the organic solvent solution of the silane coupling agent. The mass fraction of the organic solvent solution of the silane coupling agent is 1-10%.
The carbon nano tube is added by adopting a carbon nano tube dispersion liquid. The mass fraction of the carbon nano tube dispersion liquid is 1-5%.
The silane coupling agent in the step 2) is at least one of 3-aminopropyltriethoxysilane, 3- (2-aminoethylamino) propyltrimethoxysilane, 3-aminopropyldiethoxysilane, aminotrimethoxysilane and N-beta- (aminoethyl) -gamma-aminopropylmethyldimethoxysilane.
The organic solvent A in the step 2) is at least one of toluene, xylene, cyclohexane, carbon tetrachloride and N-methylpyrrolidone.
The mass ratio of the composite material A, the dispersant and the solid electrolyte in the step 3) is 100:1-3:5-10
The organic solvent B in the step 3) is at least one of isopropanol, ethanol, butanediol, n-butanol and glycerol.
The solid electrolyte comprises Li x+5 La 3 Zr 2-y A y O 12 Wherein A is at least one of Al, Ta, Ti, V, Nb, Hf, Si, Ge and Sn, x is more than 1.5 and less than 2, and y is more than 0 and less than 1.0. Further, the solid electrolyte is composed of Li x+5 La 3 Zr 2-y A y O 12 With Li 0.5 La 0.5 TiO 3 The weight ratio of the components is 6: 5.
In the step 3), the composite material A, the dispersing agent and the solid electrolyte are uniformly dispersed in the organic solvent, namely the composite material A and the dispersing agent are added into the organic solution of the solid electrolyte; the mass fraction of the organic solution of the solid electrolyte is 1-10%.
The dispersing agent in the step 3) is at least one of ethyl acetate, acetylacetone, ethyl acetoacetate, polyacrylamide, lithium polyacrylat, sodium dodecyl sulfate, methyl amyl alcohol and fatty acid polyglycol ester.
In the step 4), the temperature is raised to 700-1100 ℃ at a speed of 1-10 ℃/min and the temperature is preserved.
The inert atmosphere is argon atmosphere or nitrogen atmosphere.
The low-expansion silicon-based composite negative electrode material adopts porous nano silicon, hydroxyl/carboxyl groups are grafted on the surface of the porous nano silicon, and the structural stability of the material is improved through-CO-NH-groups which are chemically bonded and formed by an aminosilane coupling agent and carbon nano tubes of the aminosilane coupling agent, so that the isotropy of a net structure of a carbon material formed after carbonization is improved, and the expansion of silicon in the charging and discharging process is restrained. Meanwhile, the solid electrolyte in the middle layer has the characteristic of high lithium ion conductivity, and the rate capability of the material is improved. After the shell is coated with the amorphous carbon, the outermost carbon coating layer can effectively improve the conductivity of the silicon-based material, avoid direct contact of nano-silicon and electrolyte, reduce side reactions, effectively relieve the volume effect in the charging and discharging process and improve the storage performance.
Furthermore, the solid electrolyte layer can avoid direct contact between the porous nano-silicon and electrolyte, reduce side reactions, and further effectively improve the conductivity of the silicon-based material and relieve the volume effect in the charging and discharging process.
Drawings
Fig. 1 is an SEM image of a low-expansion silicon-based composite anode material prepared in example 1 of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects solved by the present invention easier to understand, the present invention will be described in detail with reference to specific embodiments.
Example 1
The low-expansion silicon-based composite negative electrode material comprises an inner core and a shell coated on the inner core, wherein the shell comprises an inner coating layer, an intermediate coating layer and an outer coating layer which are sequentially arranged from inside to outside, the inner coating layer is a carbon layer, the intermediate coating layer is a solid electrolyte layer, the outer coating layer is an amorphous carbon layer, and the mass of the shell accounts for 9% of the mass of the low-expansion silicon-based composite negative electrode material.
The preparation method of the low-expansion silicon-based composite anode material of the embodiment comprises the following steps:
1) adding 100g of nano silicon powder with the particle size of 100nm into 500mL of hydrofluoric acid solution with the mass fraction of 5% to be soaked for 3 hours, then filtering, and washing the solid with deionized water to obtain porous nano silicon;
2) adding 100g of the porous nano-silicon prepared in the step 1) into 60mL of toluene solution of 5% by mass of 3-aminopropyltriethoxysilane, then adding 100mL of mixed solution of 2% by mass of a carbon nanotube conductive agent and N-methylpyrrolidone, uniformly mixing and dispersing, then filtering, and carbonizing the solid at 800 ℃ for 3 hours in an argon inert atmosphere to obtain a composite material A;
3) mixing 8g of Li 6.7 La 3 Zr 1.3 Al 0.7 O 12 Adding the mixture into 100mL of isopropanol, uniformly dispersing to obtain a suspension of solid electrolyte with the mass fraction of 8%, then adding 100g of the composite material A prepared in the step 2) and 2g of ethyl acetate, uniformly dispersing to obtain a dispersion liquid, and performing spray drying on the dispersion liquid to obtain a composite material B;
4) transferring the composite material B prepared in the step 3) into a tubular furnace, and introducing a methane mixed gas into the tubular furnace, wherein the methane mixed gas is prepared from methane and ammonia gas according to a volume ratio of 100: 3, mixing;
then heating to 900 ℃ at the heating rate of 3 ℃/min, preserving heat for 3h, then naturally cooling to room temperature under the inert atmosphere of argon, and crushing to obtain the product.
The lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein the positive electrode comprises a positive electrode current collector and a positive electrode material layer arranged on the surface of the positive electrode current collector, the positive electrode material layer comprises a positive electrode active substance, a positive electrode conductive agent and a positive electrode binder, the positive electrode active substance is a ternary positive electrode material (NCM532), the positive electrode conductive agent is SP, the positive electrode binder is LA132, and the mass ratio of the positive electrode active substance to the positive electrode binder is 8.5:1: 0.5. The negative electrode comprises a negative electrode current collector and a negative electrode material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode material layer comprises a negative electrode active substance, a negative electrode conductive agent and a negative electrode binder, the negative electrode active substance is a mixed material of the low-expansion silicon-based composite negative electrode material prepared in the embodiment and artificial graphite according to the mass ratio of 1:9, the negative electrode conductive agent is acetylene black, and the negative electrode binder is PVDF, and the mass ratio of the acetylene black to the artificial graphite is 9:0.5: 0.5. The diaphragm is a celegard2400 diaphragm, and the electrolyte is LiPF with the concentration of 1mol/L 6 Solution, solvent is mixed by EC and DEC with the volume ratio of 1: 1).
Example 2
The low-expansion silicon-based composite negative electrode material of the embodiment comprises a core and a shell coated on the core, wherein the shell comprises an inner coating layer, a middle coating layer and an outer coating layer which are sequentially arranged from inside to outside, the inner coating layer is a carbon layer, the middle coating layer is a solid electrolyte layer, the outer coating layer is an amorphous carbon layer, and the quality of the shell accounts for 6% of the quality of the low-expansion silicon-based composite negative electrode material.
The preparation method of the low-expansion silicon-based composite anode material of the embodiment comprises the following steps of:
1) adding 100g of nano silicon powder with the particle size of 200nm into 1000mL of hydrofluoric acid solution with the mass fraction of 1%, soaking for 3h, then filtering, and washing the solid with deionized water to obtain porous nano silicon;
2) adding 100g of the porous nano-silicon prepared in the step 1) into 100mL of xylene solution of 1% by mass of 3- (2-aminoethylamino) propyl trimethoxy silane, then adding 100mL of conductive liquid of 1% by mass of N-methyl pyrrolidone of carbon nano-tubes, uniformly mixing and dispersing, then filtering, and carbonizing the solid at 800 ℃ for 3h under argon inert atmosphere to obtain a composite material A;
3) 5g of Li 6.5 La 3 Zr 1.5 Si 0.5 O 12 Adding the mixture into 500mL of cyclohexane, uniformly dispersing to obtain a solid electrolyte solution with the mass fraction of 1%, then adding 100g of the composite material A prepared in the step 2) and 1g of acetylacetone, uniformly dispersing to obtain a dispersion liquid, and performing spray drying on the dispersion liquid to obtain a composite material B;
4) transferring the composite material B prepared in the step 3) into a tubular furnace, and introducing acetylene mixed gas into the tubular furnace, wherein the acetylene mixed gas is prepared from acetylene and ammonia gas according to a volume ratio of 100:1, mixing;
and then heating to 700 ℃ at the heating rate of 1 ℃/min, preserving the heat for 6 hours, naturally cooling to room temperature under the inert atmosphere of argon, and crushing to obtain the product.
The lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein the positive electrode comprises a positive electrode current collector and a positive electrode material layer arranged on the surface of the positive electrode current collector, the positive electrode material layer comprises a positive electrode active substance, a positive electrode conductive agent and a positive electrode binder, the positive electrode active substance is a ternary positive electrode material (NCM532), the positive electrode conductive agent is SP, the positive electrode binder is LA132, and the mass ratio of the positive electrode active substance to the positive electrode binder is 8.5:1: 0.5. The negative electrode comprises a negative electrode current collector and a negative electrode material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode material layer comprises a negative electrode active substance, a negative electrode conductive agent and a negative electrode binder, the negative electrode active substance is a mixed material of the low-expansion silicon-based composite negative electrode material prepared in the embodiment and artificial graphite according to the mass ratio of 1:9, the negative electrode conductive agent is acetylene black, and the negative electrode binder is PVDF, and the mass ratio of the acetylene black to the artificial graphite is 9:0.5: 0.5. The diaphragm is a celegard2400 diaphragm, and the electrolyte is LiPF with the concentration of 1mol/L 6 Solution, solvent is mixed by EC and DEC with the volume ratio of 1: 1).
Example 3
The low-expansion silicon-based composite negative electrode material comprises an inner core and a shell coated on the inner core, wherein the shell comprises an inner coating layer, an intermediate coating layer and an outer coating layer which are sequentially arranged from inside to outside, the inner coating layer is a carbon layer, the intermediate coating layer is a solid electrolyte layer, the outer coating layer is an amorphous carbon layer, and the mass of the shell accounts for 12% of the mass of the low-expansion silicon-based composite negative electrode material.
The preparation method of the low-expansion silicon-based composite anode material of the embodiment comprises the following steps:
1) adding 100g of nano silicon powder with the particle size of 500nm into 1000mL of 10% hydrofluoric acid solution for soaking for 3h, then filtering, and washing the solid with deionized water to obtain porous nano silicon;
2) adding 100g of the porous nano-silicon prepared in the step 1) into 50mL of a carbon tetrachloride solution of 3-aminopropyldiethoxysilane with the mass fraction of 10%, then adding 200mL of N-methylpyrrolidone conducting solution of a carbon nanotube conducting agent with the mass fraction of 5%, uniformly mixing and dispersing, then filtering, and carbonizing the solid at 800 ℃ for 3h under the inert atmosphere of argon to obtain a composite material A;
3) mixing 8g of Li 6.9 La 3 Zr 1.9 Ti 0.1 O 12 Adding the mixture into 80mL of glycerol, uniformly dispersing to obtain a solid electrolyte solution with the mass fraction of 10%, then adding 100g of the composite material A prepared in the step 2) and 3g of sodium dodecyl sulfate, uniformly dispersing to obtain a dispersion liquid, and performing spray drying on the dispersion liquid to obtain a composite material B;
4) transferring the composite material B prepared in the step 3) into a tubular furnace, and introducing ethylene mixed gas into the tubular furnace, wherein the ethylene mixed gas is prepared by mixing ethylene and ammonia gas according to a volume ratio of 100: 5, mixing the components;
heating to 1100 deg.C at a heating rate of 5 deg.C/min, maintaining for 1h, naturally cooling to room temperature under inert atmosphere of argon, and pulverizing.
The lithium ion battery of this embodiment is the same as the lithium ion battery of embodiment 1, except that the low-expansion silicon-based composite negative electrode material prepared in this embodiment is used.
Example 4
The low-expansion silicon-based composite negative electrode material comprises an inner core and a shell coated on the inner core, wherein the shell comprises an inner coating layer, an intermediate coating layer and an outer coating layer which are sequentially arranged from inside to outside, the inner coating layer is a carbon layer, the intermediate coating layer is a solid electrolyte layer, the outer coating layer is an amorphous carbon layer, and the mass of the shell accounts for 8.8% of the mass of the low-expansion silicon-based composite negative electrode material.
The preparation method of the low-expansion silicon-based composite anode material of the embodiment comprises the following steps:
1) adding 100g of nano silicon powder with the particle size of 100nm into 1000mL of hydrofluoric acid solution with the mass fraction of 3% for soaking for 3h, then filtering, washing the solid with deionized water, and drying to obtain porous nano silicon;
2) adding 100g of the porous nano-silicon prepared in the step 1) into 120mL of toluene solution of N-beta- (aminoethyl) -gamma-aminopropylmethyldimethoxysilane with the mass fraction of 5%, then adding 80mL of carbon nano tube conductive agent mixed solution with the mass fraction of 2%, uniformly mixing and dispersing, then filtering, preserving the temperature of the solid at 360 ℃ for 2h under the inert atmosphere of argon, and then carbonizing at 800 ℃ for 3h to obtain a composite material A;
3) mixing 6g of Li 6.5 La 3 Zr 1.5 Ge 0.5 O 12 Adding the mixture into 100mL of isopropanol, uniformly dispersing to obtain a mixed solution of solid electrolyte with the mass fraction of 6%, then adding 100g of the composite material A prepared in the step 2) and 2g of ethyl acetate, uniformly dispersing to obtain a dispersion liquid, carrying out spray drying on the dispersion liquid, adding the obtained particles into ammonia water with the mass fraction of 5%, soaking for 1h, then adding a copper nitrate solution with the mass fraction of 15%, soaking for 3h, filtering, and drying to obtain a composite material B;
4) transferring the composite material B prepared in the step 3) into a tubular furnace, and introducing a methane mixed gas into the tubular furnace, wherein the methane mixed gas is prepared from methane and ammonia gas according to a volume ratio of 100: 5, mixing the components;
then heating to 900 ℃ at the heating rate of 7 ℃/min, preserving heat for 3h, then naturally cooling to room temperature under the inert atmosphere of argon, and crushing to obtain the product.
The lithium ion battery of this embodiment is the same as the lithium ion battery of embodiment 1, except that the low-expansion silicon-based composite negative electrode material prepared in this embodiment is used.
Example 5
The difference between this embodiment and embodiment 4 is that step 3) is: mixing 6g of Li 6.5 La 3 Zr 1.5 Ge 0.5 O 12 With 5g of Li 0.5 La 0.5 TiO 3 Adding the mixture into 100mL of isopropanol, uniformly dispersing to obtain a mixed solution of 11% by mass of solid electrolyte, then adding 100g of the composite material A prepared in the step 2) and 2g of ethyl acetate, uniformly dispersing to obtain a dispersion liquid, and carrying out spray drying on the dispersion liquid to obtain a composite material B.
The rest is the same as in example 4.
Comparative example
The preparation method of the silicon-based composite anode material comprises the following steps:
1) adding 100g of nano silicon powder with the particle size of 100nm into 500mL of hydrofluoric acid solution with the mass fraction of 5% for soaking for 3h, then filtering, and washing the solid with deionized water to obtain porous nano silicon;
2) weighing 100g of the porous nano silicon material prepared in the step 1), transferring the porous nano silicon material into a tubular furnace, introducing methane gas, heating to 900 ℃ at a heating rate of 3 ℃/min, preserving heat for 3h, naturally cooling to room temperature under an argon inert atmosphere, and crushing to obtain the porous nano silicon material.
The lithium ion battery of this comparative example was the same as example 1.
Examples of the experiments
1. Physical and chemical testing
(1) Topography testing
The silicon-based composite material of example 1 was subjected to SEM test, and the test results are shown in fig. 1.
As can be seen from FIG. 1, the material has a granular structure, and the particle size distribution of the material is uniform and reasonable, and the amorphous carbon material is arranged among the particles, and the particle size of the particles is between 2 and 8 μm.
(2) The specific surface area, tap density, carbon content and trace element content (La/Ti/Zr/Ti/Si/Al) of the silicon-based composite material are tested by referring to GB/T38823-.
The test results are shown in table 1.
2. Electrochemical Performance test
(1) Button cell test
Button cells were prepared by using the silicon-based composite negative electrode materials of examples 1 to 5 and comparative example as negative electrode materials of lithium ion batteries according to the following methods, which are respectively marked as a1, a2, A3 and B1:
adding a binder, a conductive agent and a solvent into the silicon-based composite material, stirring and pulping, coating the mixture on a copper foil, and drying and rolling to prepare a negative plate; the used binder is LA132, the conductive agent is SP, the solvent is NMP, and the dosage ratio of the negative electrode material, SP, PVDF and NMP is 95g:1g:4g:220 mL; the electrolyte is LiPF 6 The electrolyte solution is 1mol/L, wherein the solvent is a mixture of EC and DEC with the volume ratio of 1: 1; the metal lithium sheet is a counter electrode, and the diaphragm is a polypropylene (PP) film. Button cell assembly was performed in an argon-filled glove box.
The electrochemical performance is carried out on a Wuhan blue electricity CT2001A type battery tester, the charging and discharging voltage range is 0.005V to 2.0V, and the charging and discharging rate is 0.1C.
The test results are shown in table 1.
TABLE 1 silicon-based composite negative electrode material test Performance
As can be seen from the data in Table 1, the specific capacity and the first efficiency of the silicon-based composite material prepared by the invention are obviously superior to those of the comparative example. The reasons for this may be: by coating the surface of the core porous nano silicon with the coupling agent, the coupling agent can improve the connection degree between raw materials after being mixed, so that the carbon source branched chain is solidified, and a more complex three-dimensional network structure is generated after carbonization; the solid electrolyte provides sufficient lithium ions and reduces irreversible capacity loss thereof to improve the first efficiency of the material; meanwhile, the material of the coating layer of the middle layer contains organic matters, and the organic matters are carbonized to form amorphous carbon, so that the content of carbon is increased, and the tap density and the powder conductivity of the material are increased.
(2) Testing the soft package battery:
the silicon-based composite materials in examples 1-5 and comparative example and artificial graphite are mixed according to the mass ratio of 1:9 to be used as a negative electrode material to prepare a negative electrode plate, and 5Ah soft package batteries are prepared according to the description in the examples and are marked as C1, C2, C3, C4, C5 and D1. And respectively testing the liquid absorption and retention capacity of the negative pole piece, the full-electric rebound and the cycle performance of the pole piece.
a. Imbibition ability test
And (3) adopting a 1mL burette, sucking the electrolyte VmL, dripping a drop on the surface of the pole piece, timing until the electrolyte is completely absorbed, recording the time t, and calculating the liquid absorption speed V/t of the pole piece.
The test results are shown in table 2.
b. Liquid retention test
Calculating theoretical liquid absorption amount m of the pole piece according to pole piece parameters 1 And weighing the weight m of the pole piece 2 Then, the pole piece is placed in electrolyte to be soaked for 24 hours, and the weight of the pole piece is weighed to be m 3 Calculating the liquid absorption m of the pole piece 3 -m 2 And calculated according to the following formula: retention rate ═ m 3 -m 2 )*100％/m 1 。
The test results are shown in table 2.
TABLE 2 test of the liquid retention property of the pole piece washing liquid
As can be seen from Table 2, the liquid-absorbing and liquid-retaining abilities of the silicon composite materials obtained in examples 1 to 5 were significantly higher than those of the comparative example. The reason for this may be: the specific surface of the composite material of the embodiment is larger, so that the liquid absorption and retention capacity of the material is improved.
c. Pole piece full-electric rebound rate test
Firstly testing the rolled thickness of the pole piece to be D1, then fully charging the battery to 100% SOC, then unblanking the pole piece and testing the average thickness to be D2, and calculating according to the following formula: the rebound rate was (D2-D1) × 100%/D1.
The test results are shown in table 3.
d. Pole piece resistivity testing
The resistivity of the pole piece was measured using a resistivity tester, and the results are shown in table 3.
TABLE 3 Pole piece resistance and rebound Rate testing
| Full charge rebound rate of pole piece (%) | Pole piece resistivity (m omega) | |
| Example 1 | 32.8 | 16.8 |
| Example 2 | 33.6 | 17.9 |
| Example 3 | 31.1 | 20.1 |
| Example 4 | 34.1 | 23.5 |
| Example 5 | 34.5 | 24.2 |
| Comparative example 1 | 42.6 | 198.5 |
As can be seen from the data in Table 3, the full-charge rebound rate and the specific resistance of the negative electrode prepared by using the silicon agent composite materials obtained in examples 1 to 5 are obviously lower than those of the comparative example, namely, the negative electrode sheet prepared by using the composite material of the invention has lower rebound rate and specific resistance. The reason for this may be: the surface of the material of the embodiment is coated with the expansion of the solid electrolyte binding material and is carbonized to form a chemical bond after being connected with a coupling agent, so that the expansion is reduced; meanwhile, the pole piece material of the embodiment material contains a conductive agent with high electronic conductivity, and the outer layer of the pole piece material is doped with nitrogen atoms to reduce the electronic conductivity of the material.
e. Cycle performance test
The cycle performance of the battery is tested at the temperature of 25 +/-3 ℃ with the charge-discharge multiplying power of 0.5C/1C and the voltage range of 2.5V-4.2V.
The test results are shown in table 4.
f. Rate capability test
Constant current and constant voltage charging were performed at a rate of 2C, and then the constant current ratio of the battery was calculated.
The test results are shown in table 4.
TABLE 4 electrochemical Performance test
| Battery with a battery cell | Capacity retention (%) after 500 cycles | 2C constant current ratio |
| C1 | 94.62 | 85.7％ |
| C2 | 93.78 | 85.1％ |
| C3 | 94.69 | 84.9％ |
| C4 | 94.02 | 84.2％ |
| C5 | 93.89 | 83.9％ |
| D1 | 86.55 | 81.7％ |
As can be seen from table 4, the cycling performance of the cell made of the silicon-based composite material of the present invention is significantly better than that of the comparative example, which may be due to: the pole piece prepared from the silicon-based composite material has a low expansion rate, the structure of the pole piece is more stable in the charging and discharging processes, and the cycle performance of the pole piece is improved. In addition, the solid electrolyte coated on the surface of the silicon-carbon composite material and the nitrogen-doped amorphous carbon have the characteristics of high density and strong structural stability, and the cycle performance of the solid electrolyte is also improved. Meanwhile, as the material coating layer contains solid electrolyte with high lithium ion conductivity, the quick charge performance of the material is improved.
Claims (10)
1. The low-expansion silicon-based composite negative electrode material is characterized by comprising an inner core and a shell coated on the inner core, wherein the shell comprises an inner coating layer, a middle coating layer and an outer coating layer which are sequentially arranged from inside to outside, the inner coating layer is an amorphous carbon layer A, the middle coating layer is a solid electrolyte layer, the outer coating layer is an amorphous carbon layer B, and the mass of the shell accounts for 5-15% of the mass of the low-expansion silicon-based composite negative electrode material.
2. The preparation method of the low-expansion silicon-based composite anode material is characterized by comprising the following steps of:
1) soaking the silicon powder in hydrofluoric acid for 2-5h, and carrying out solid-liquid separation to obtain porous silicon;
2) uniformly mixing the porous silicon obtained in the step 1), a silane coupling agent and a carbon nano tube in an organic solvent A, and then carrying out carbonization treatment to obtain a composite material A; the carbonization treatment is carried out for 3-5h at the temperature of 750-800 ℃ in inert atmosphere;
3) uniformly dispersing the composite material A obtained in the step 2), a dispersing agent and a solid electrolyte in an organic solvent B, and then carrying out spray drying to obtain a composite material B;
4) preserving the temperature of the composite material B obtained in the step 3) in a carbon source mixed gas at 700-; the carbon source mixed gas is formed by mixing at least one of methane, ethylene and acetylene with ammonia gas according to the volume ratio of 100: 1-10.
3. The preparation method of the low-expansion silicon-based composite anode material as claimed in claim 2, wherein the particle size of the silicon powder in the step 1) is 100-500 nm.
4. The preparation method of the low-expansion silicon-based composite anode material as claimed in claim 2, wherein the mass ratio of the porous silicon to the silane coupling agent to the conductive agent in step 2) is 100: 1-5: 0.5-2.
5. The method for preparing the low-expansion silicon-based composite anode material as claimed in claim 4, wherein the silane coupling agent in the step 2) is at least one of 3-aminopropyltriethoxysilane, 3- (2-aminoethylamino) propyltrimethoxysilane, 3-aminopropyldiethoxysilane, aminotrimethoxysilane, and N-beta- (aminoethyl) -gamma-aminopropylmethyldimethoxysilane.
6. The preparation method of the low-expansion silicon-based composite anode material as claimed in claim 2, wherein the mass ratio of the composite material A, the dispersant and the solid electrolyte in the step 3) is 100:1-3: 5-10.
7. The method for preparing the low-expansion silicon-based composite anode material according to claim 6, wherein the solid electrolyte comprises Li x+5 La 3 Zr 2-y A y O 12 Wherein A is at least one of Al, Ta, Ti, V, Si, Ge and Sn, x is more than 1.5 and less than 2, and y is more than 0 and less than 1.0.
8. The preparation method of the low-expansion silicon-based composite anode material as claimed in claim 7, wherein the step 3) of uniformly dispersing the composite material A, the dispersant and the solid electrolyte in the organic solvent is to add the composite material A and the dispersant into an organic solution of the solid electrolyte; the mass fraction of the organic solution of the solid electrolyte is 1-10%.
9. The method for preparing the low-expansion silicon-based composite anode material as claimed in claim 2, wherein the temperature in the step 4) is raised to 700-1100 ℃ at a rate of 1-10 ℃/min.
10. A lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, and is characterized in that the negative electrode comprises a negative electrode current collector and a negative electrode material layer arranged on the surface of the negative electrode current collector, the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material is the low-expansion silicon-based composite negative electrode material in claim 1.
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